Invasive Plant Science and Management 2017 10:166–179 © Weed Science Society of America, 2017. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.

Regulation of the Invasive Plant Heracleum persicum by Private Landowners in Tromsø, Norway

Sophie Meier, Gregory N. Taff, Jens B. Aune and Sebastian Eiter*

In the city of Tromsø in northern Norway, invasive Tromsø palm (Norwegian: Tromsøpalme; English: Persian hogweed) is widespread. Although Tromsø palm has negative impacts on biodiversity and contains a phototoxic sap that burns human skin, it is also considered to be a local symbol of Tromsø city and is appreciated by many inhabitants. This study examined private landowners’ characteristics, perceptions, and landowners’ regulation of invasive Tromsø palm on their parcels on Tromsø Island in 2012 (vegetation season: May–September) to provide information concerning which landowner groups could be assisted by official regulation. Eleven key informants and 17 landowners were inter- viewed. Afterward, Tromsø palm on Tromsø Island was mapped using aerial photos and street-level photos from Google ® ® Maps /Google Street View and fieldwork verification. This distribution map was superimposed on a property map in a geographic information system to produce a map showing private parcels that contained Tromsø palm and associated neighboring parcels that did not contain Tromsø palm. Questionnaires were mailed to the 441 owners of the selected parcels, and 199 of the returned questionnaires were analyzed. Tromsø palm was more likely to be fully regulated/absent on a parcel that was inhabited (particularly if the owner lived on-site) and less likely to be fully regulated/absent if the parcel was jointly managed by several households. These findings indicate that authorities could focus their management efforts on supporting regulation efforts of those private landowners who own currently uninhabited or rented-out parcels and landowners of parcels jointly managed by several households.Furthermore,thoselandowners who found regulation measures against the plant on Tromsø Island important tended to have partly or fully regulated Tromsø palm on their plots. This might imply that information campaigns from authorities might encourage more landowners to regulate Tromsø palm. Nomenclature: Tromsø palm (Norwegian: Tromsøpalme; English: Persian hogweed); Heracleum persicum Fischer/ H. laciniatum auct. scand.; non Hornem. Key words: Hogweed, invasive plants, invasive species management, invasive species mapping, landowner plant regulation behavior.

Globalization has moved the issue of alien and invasive spread more than 100 m from the parent plant within less species into the focus of public and scientific attention than 50 yr (Richardson et al. 2000). The International (McNeely 2001a). “Alien plants” include all plant species that Union for Conservation of Nature and Natural Resources are nonnative to an area and brought there by humans. additionally defines “invasive species” as species that negatively “Invasive plants” are alien plants that are able to spread over a impact ecosystems and/or human health and that lead to high relatively wide distance within a relatively short time period in economic costs (McNeely et al. 2001). the area where they were introduced, e.g., seed plants that The number of alien plants introduced after 1500 CE (neophytes) has grown with the size of cities in Central DOI: 10.1017/inp.2017.11 Europe (Pyšek 1998). This could be due to the fact that in * First and third authors: Forest information systems employee, For- densely populated areas, seeds of alien plants can be easily estry Research and Competence Center, Jägerstrasse 1, 99867 Gotha, spread by displacement of soil and via car tires. Also, alien Germany; second and fourth authors: Research Scientist and Research plant species were planted in gardens from which they could Scientist, Norwegian Institute for Bioeconomy Research, P.O. Box 115, escape and grow in the wild (Hodkinson and Thompson N-1431 Ås, Norway. Corresponding author’s E-mail: meier.so@ 1997). In the city of Tromsø in northern Norway, an t-online.de invasive Heracleum species, called “Tromsøpalme” in

166 • Invasive Plant Science and Management 10, April–June 2017

Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 27 Sep 2021 at 18:01:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/inp.2017.11 Management Implications This study identified private landowners in the city of Tromsø, Norway who do not or only partially regulate invasive Tromsø palm on their parcels, enabling the plant to spread to other parcels. These landowners could be considered primary candidates for education and support by authorities, given limited resources to control the weed. According to the results, private landowners who own currently uninhabited or rented-out parcels would be good candidates to receive financial incentives or other assistance, since the successful management of the plant demands frequent attention and action. Furthermore, the municipality should consider targeting landowners of recently acquired parcels and provide active help and education regarding how to manage the plant in the first years of ownership. Owners of jointly owned parcels were also found to be appropriate candidates to receive plant management assistance. At the same time, the authorities can develop priority areas to focus Tromsø palm control efforts, such as private lands Figure 1. Tromsø palm growing along the wall of a house in close to public areas, to reduce potential spread onto public lands, Tromsø city, August 2012. (Photo: S. Meier) and high-population areas, to reduce risk for injuries. It was shown in the study that some landowners deposit plant waste on their plots instead of using the garbage bin or the municipal fl waste-disposal site. This can lead to a further spread of the plant on white owers (Lid and Lid 2005) during the summer months their parcels. Landowners were also found to neglect tending (Fröberg 2010). The plant is perennial, reproduces only by specific areas on their parcels such as border areas or spaces that are seeds, and is polycarpic, which means it can produce seeds hidden or inaccessible, e.g., behind garages or on steep slopes. several times in its life (EPPO/OEPP 2009; Often and Graff Authorities might provide assistance or hold information campaigns on regulation of Tromsø palm in neglected areas and proper 1994). A single plant produces 6,000 to 8,000 seeds per season disposal of plant waste. Officials could improve landowners’ control (Alm and Often 2006). measures at parcel borders by encouraging coordination among The seeds of H. persicum can be dispersed by car tires, wind, landowners and providing education in neighborhood meetings. and water currents. Therefore, the plant is now frequently This study also showed that landowners who perceived Tromsø found in Tromsø along roads and beaches; however, it is also palm as a problem on Tromsø Island and those who believed in the necessity of regulation measures on Tromsø Island were more likely abundant in the city center (Alm et al. 2006; Alm and to have no Tromsø palm or fully controlled Tromsø palm on their Often 2006), growing in gardens, neglected green areas, and property. This may imply that education and information ditches (see also Figure 1). Inadequate prevention when new campaigns about the negative effects of invasive species could roads were built might also have contributed to its spread (key motivate private landowners to take action. informant: Norwegian Public Road Administration [NPRA, Norwegian: Statens vegvesen] personal communication 2012). For many garden owners in Tromsø, Tromsø palm lost its Norwegian (Heracleum persicum Fischer, Heracleum attractiveness as a garden plant because it was difficult to pre- laciniatum auct. scand., non Hornem.), has spread widely vent it from spreading throughout and beyond the garden. since it was introduced there in the 19th century as an Therefore, many garden owners cut down the plants and ornamental garden plant (Alm and Jensen 1993; Nilsen thoughtlessly threw the plant waste (including mature seeds) 1991). Population genetic analyses showed that Tromsø on adjacent parcels, thereby contributing to the uncontrolled palm seeds were probably brought from Iran via Great spread of the plant on Tromsø Island (key informants: Britain and Finland to northern Norway (Rijal et al. 2015). Green Warriors of Norway [GWN, Norwegian: Norges Jahodová et al. (2007) found that Tromsø palm probably is Miljøvernforbund] and Tromsø University personal commu- identical to H. persicum. The plant can be found in Iran, nication 2012). Iraq, and Turkey (European and Mediterranean Plant Pro- Since the end of the 1990s, officials and the key tection Organization/Organisation Européenne et Médi- informant of GWN have begun to worry about the ecological terranéenne pour la Protection des Plantes [EPPO/OEPP] impacts and the high density of Tromsø palm in Tromsø (key 2009), and this scientific name is therefore used in informants: GWN and Troms County governor [Norwegian: this paper. Fylkesmannen i Troms] personal communication 2012). Tromsø palm (Heracleum persicum)belongstothefamilyof Tromsø palm alters cultural landscapes and changes the Apiaceae (Lid and Lid 2005). It has a 1- to 4-cm-wide hollow species composition in the habitats it spreads into (Alm and stem with purple-red spots; the lower part of the stem is often Jensen 1993). It has been shown on a local scale that Tromsø completely purple-red. The plant can grow to 1- to 4-m high palm shades out other plants (Myrås and Junttila 1981) and, (EPPO/OEPP 2009; Often and Graff 1994). It produces under laboratory conditions, Tromsø palm seeds constrained

Meier et al.: Regulation of H. persicum by Private Landowners • 167

Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 27 Sep 2021 at 18:01:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/inp.2017.11 the growth of neighboring plants by producing suppressive plant from setting seeds (Nielsen et al. 2005). However, substances (allelopathy) (Junttila 1975). It would be espe- while no such research has been done on H. persicum, cially problematic if Tromsø palm were to spread beyond research with H. mantegazzianum showed that, even if urban and human-altered areas into undeveloped natural umbels are cut before seeds ripen, they are still able to locations or conservation areas in and around Tromsø (Alm develop viable seeds (Pyšek et al. 2007a), so appropriate and Jensen 1993). Due to its negative impacts on biodi- disposal of the umbels is important (Pyšek et al. 2007b). To versity, Tromsø palm has been registered by the Norwegian remove invasive Tromsø palm by mowing and cutting of the Biodiversity Information Center (Norwegian: Artsdata- stems, it is important that the plants are treated at least three banken) as a high-risk species on the Norwegian blacklist of times during the growing season (Renna 2002) for not less invasive species (Gederaas et al. 2012). than 5 yr, which exhausts the plant until it finally dies Aside from Tromsø palm’s impact on other plant species, (Nielsen et al. 2005). The plants can also be plowed or the its sap contains furocoumarins (Kavli and Volden 1984) roots can be dug out; the latter usually kills the plant that, in combination with UV radiation (e.g., from the sun), immediately. Cattle and sheep can graze on the area when the lead to a phototoxic reaction that burns human skin plants sprout at the beginning of the growing season. Finally, (photodermatitis) (Kavli et al. 1983b). The affected part of herbicides are recommended. In all cases, control of the weed the skin can develop blisters (Kavli et al. 1983b) followed by can be dangerous due to the risk of coming in contact with high melanin production (hyperpigmentation) that can the phototoxic sap (see previous discussion of furocoumarins; last for several months (Kavli et al. 1983a). Children playing Nielsen et al. 2005; key informant: Tromsø Municipality outdoors and people working outside, such as gardeners, are personal communication 2012). especially in danger of exposure to Heracleum sap (Nielsen Currently, Tromsø palm is widespread in Tromsø and et al. 2005). Various Heracleum species throughout Europe therefore it is a difficult task to regulate this plant (key infor- and North America (e.g., giant hogweed [Heracleum mants: Tromsø Municipality and Tromsø University personal mantegazzianum Sommier & Levier], Sosnowskyi’s communication 2012). At the time this study was being con- hogweed [Heracleum sosnowskyi]) present similar challenges ducted, authorities in Tromsø such as the NPRA, the Tromsø (EPPO/OEPP 2009; Nielsen et al. 2005). County governor, and Tromsø Municipality had planned or The vigorous growth of the plant and its pervasiveness in had already tried to reduce Tromsø palm in some areas. Due to Tromsø are probably the reasons why the plant was called a lack of staff and limited financial resources, the authorities only “palm” and named after the city (Alm 2006). Furthermore, regulate Tromsø palm sporadically in some specificareasin for some residents, the plant is a symbol of Tromsø and brings Tromsø (key informants: GWN, NPRA, Troms County about a sense of local identity (key informants: Tromsø Arts governor, and Tromsø Municipality personal communication Association [Norwegian: Kunstforeningen Tromsø], Troms 2012). The municipality of Tromsø handles Tromsø palm as County governor, and Tromsø University personal commu- part of the normal roadside mowing and as part of the main- nication 2012). The plant is a popular motif in works of tenance processes in graveyards and parks (key informant: artists, on postcards, for decoration (Alm 2006, 2013), and Tromsø Municipality personal communication 2012). The also for embroidery on a traditional folk costume of Tromsø NPRA tries to inhibit Tromsø palm from spreading beyond (“Tromsø festdrakt”), a costume which has been fabricated Tromsø city by focusing on large roads. NPRA made plans to since ca. 1980. Furthermore, a home for the elderly in mow invasive plants along larger roads at a breadth of Tromsø is called “Heracleum” (Tromsø Municipality 3 m several times during the growing period in future years. [Norwegian: Tromsø kommune] 2015). In the native home Additionally, NPRA wants to obtain permission from land- range (Iran), part of the plant is used for medication and as owners to remove invasive plants on private land close to the food (Hemati et al. 2010), and artists from the Tromsø Arts roads when there is a risk that invasive plants may spread from Association even invited locals to taste soup that included private parcels to roadsides (key informants: NPRA and Troms Tromsø palm as an ingredient (Hansen 2014). The proble- County governor personal communication 2012). Overall, matic aspects of Tromsø palm on the one hand and its local official regulation measures in Tromsø have not been con- importance as a symbol on the other hand have generated ducted on a large scale and are often not done persistently ambivalence toward the plant among locals (key informants: enough to reduce the overall amount of Tromsø palm in the Tromsø Arts Association, GWN, and Tromsø University area, with the exception of some specific isolated areas (key personal communication 2012); the locals in Tromsø are said informants: NPRA, Troms County governor, and Tromsø to either “love or hate” Tromsø palm (Alm 2013: 42). Municipality personal communication 2012). The removal of Tromsø palm is time-consuming and Controlling invasive plants is especially difficult in areas demands careful and persistent measures (Nielsen et al. where multiple landowners are involved (Gardener et al. 2005). One way to inhibit the further spread of tall invasive 2010). There are no widely applied official measures to Heracleum,suchasTromsøpalmorH. mantegazzianum, regulate Tromsø palm on private land; Tromsø authorities is to cut the umbels when they begin to flower to prevent the rely on informing private landowners about health risks and

168 • Invasive Plant Science and Management 10, April–June 2017

Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 27 Sep 2021 at 18:01:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/inp.2017.11 methods of regulation. One reason for this might be that and normative beliefs related to private landowners’ parcels there is no jurisdiction for the public authorities to regulate that lead to spread of Tromsø palm, e.g., by not thoroughly the plant on private land. Furthermore, concern about regulating Tromsø palm? This study gives insight about the the plant among most officials is not sufficiently high types of private parcels in an urban area that may contribute (key informants: Troms County governor, GWN, and more to the spread of Tromsø palm than others. Tromsø Municipality personal communication 2012). Management plans often do not consider that, e.g., an invasive plant might be perceived as a useful and ornamental Materials and Methods garden plant by some locals and might have other positive aspects, such as an emotional meaning or having some Study Area. The study area is Tromsø Island (Norwegian: economic value; therefore, support for control programs by Tromsøya, 69.40°N, 18.56°E), which includes the city locals can be low (Blossey 1999; Gardener et al. 2010; center of Tromsø, some residential and port areas, and parks Rotherham and Lambert 2011). Management strategies (Figure 2). Tromsø Island was chosen as the actual study site fi should therefore incorporate public perception of invasive because it is a clearly de ned area and contains the majority species (Aitken et al. 2009; McNeely 2001b; Qvenild et al. of the city. Tromsø lies in the county of Troms and is the 2014; Rotherham and Lambert 2011; van Wilgen 2012). largest town in northern Norway with 67,969 inhabitants Daab and Flint (2010) and Fischer and Charnley (2012) (year: 2012); more than half of these inhabitants (36,088) found that among private (forest) landowers, those who said lived on Tromsø Island (Statistics Norway 2016). Tromsø they were bothered by invasive plants were significantly more Island is approximately 10-km long and up to 3.6-km wide likely to take action against them on their properties. Addi- and ranges in altitude from 0 to 160 m. Tromsø has a tionally, Fischer and Charnley (2012) found that owners who humid subarctic climate. have their principal residences on a parcel tend to take sig- nificantly more action against invasive plants on that parcel. Data Collection. Data were collected between June 2012 Research found that values and normative beliefs can play a and March 2013. At first, semistructured interviews with 11 role in behavioral decisions (e.g., Ajzen and Fishbein 1977; key informants in Tromsø were conducted. The first key Homer and Kahle 1988), decisions regarding environmentally informants were selected from authors of literature about friendly behavior (e.g., Kollmuss and Agyeman 2002), and Tromsø palm in Tromsø. Subsequently, key informants were supporting decisions regarding wildlife management (Bright selected by snowball sampling: key informants provided and Manfredo 1996; Vaske and Donnelly 1999). contacts to more key informant interviewees (Marshall 1996). In this study, we investigate how private landowners’ A main criterion for sampling was that the key informants regulation behavior is determined by the landowners’ had worked with Tromsø palm in some way. Furthermore, sociodemographic and parcel characteristics and the private it was important to get a range of different opinions, views, landowners’ evaluation of Tromsø palm’s values and of experiences, and factual knowledge concerning the plant. normative beliefs regarding how Tromsø palm should be The key informants were asked about different aspects of managed on Tromsø Island. Values describe positive or Tromsø palm (distribution, history, biology, etc.) and how negative feelings toward something, such as “good or bad” locals perceive and regulate it. Key informants came from or “ugly or beautiful” (Rokeach 1979:16). For this study, authorities in Tromsø (NPRA, Troms County governor, and the “aesthetic value” (the appearance of Tromsø palm is Tromsø Municipality), an environmental organization evaluated as either ugly or nice) and the “symbolic value” (GWN), Tromsø University, and the Tromsø Arts Association. (whether or not Tromsø palm is perceived as an important Furthermore, a local Tromsø palm enthusiast was interviewed. symbol of Tromsø) are used as defined by Kellert (1996: In addition, 17 private landowners and 3 renters were inter- 14–20). A further value created for this study is the “health viewed to gather anecdotal information. The interviews were value,” which addresses whether Tromsø palm is evaluated analyzed by identifying topics in the text through “descriptive as being good or dangerous to human health. Normative coding” and “initial coding” (Saldaña 2013: 87–105). beliefs in this study refer to whether landowners generally Analysis of the interviews informed the development of considered Tromsø palm’s occurrence on Tromsø Island a self-administered questionnaire that was subsequently as problematic and, more specifically, whether regulation of mailed to a sample of private landowners on Tromsø Island. Tromsø palm on Tromsø Island undertaken by local To maximize statistical power, an almost even number of institutions is seen as necessary and to what degree Tromsø landowners in the sample were gathered who had the plant palm should be removed. Normative beliefs describe what on their parcels (did not regulate it sufficiently, and thus it somebody thinks somebody else is supposed to do or not to was visible in the field in the growing season 2012) and do (Fishbein and Ajzen 1975; Zinn et al. 1998). private landowners who did not have the plant on their The specific research issues we address are: How are parcels (or regulated it, so that it was not visible in the field sociodemographic characteristics, parcel characteristics, values, in the 2012 growing season).

Meier et al.: Regulation of H. persicum by Private Landowners • 169

Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 27 Sep 2021 at 18:01:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/inp.2017.11 Figure 2. Case–control sampling of private parcels on Tromsø Island, southern area of Tromsø city (Map source: Norwegian Insti- tute of Bioeconomy Research). Status of classification of parcels with Tromsø palm and corresponding parcels without Tromsø palm ® (chosen in a 20-m radius) based on author’s classification by visual interpretation of parcels using Google Maps and Google Street ® View . This map was used for field visits to verify the classification of the parcels.

To obtain the sample of landowners, Tromsø palm was neighboring parcel without Tromsø palm (control) within mapped on Tromsø Island in ESRI ArcGIS 10. Information a 20-m radius was randomly selected from the parcel map to about the distribution of Tromsø palm on Tromsø Island achieve a case–control approach. The goal was to have ® was obtained from aerial photos from Google Maps (year: randomly selected control parcels located in the neighbor- ® 2007) and street photos from Google Street View (year: hood of the cases (Schlesselman 1982) (Figure 2). All 2010) (Google Earth 7. 1. 1. 2013; Google Maps 2017). resulting 441 parcels were surveyed in the field (July to With the help of a cadastral map and an address file (from September 2012), and the classification of the parcels the Norwegian Mapping Authority), all private parcels on (regarding whether or not Tromsø palm was visible on the Tromsø Island that contained Tromsø palm were identified parcels) was verified and corrected if necessary. and included in the sample (therefore the private parcels Forexample,ifanon-TP-parcel(parcelwithoutTromsø ® ® with Tromsø palm represent a census on Tromsø Island). palm), classified through Google Maps /Google Street View , For all parcels with Tromsø palm (case), one private was found in the field to be a TP-parcel (parcel with Tromsø

170 • Invasive Plant Science and Management 10, April–June 2017

Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 27 Sep 2021 at 18:01:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/inp.2017.11 palm), its classification was changed to “TP-parcel.” Then, two During initial fieldwork, we found that landowners with new neighboring non-TP-parcels were selected arbitrarily in Tromsø palm regulated it to varying degrees. Therefore, the field within 20 m of the original and newly identified landowners were asked in the questionnaire to specify TP-parcel. In the case of a wrongly classified TP-parcel, two how much they regulated Tromsø palm between May and new neighboring TP-parcels needed to be chosen. September 2012: “full regulation, no plant flowered”; The questionnaire was developed as a brochure and “partial regulation, at least one plant flowered (which means pretested on landowners during fieldwork. The questionnaire the plant could still spread)”; “no regulation, the plant could was revised based on feedback from these tests. The grow and spread unhindered on the parcel.” The regulation questionnaire included sections on the following five topics: behavior was also categorized according to the parcels’ (1) parcel characteristics (if the owner vs. only a renter/renters contribution to the potential spread of Tromsø palm lived on the parcel or if it was uninhabited, the length of (full regulation or Tromsø palm absent vs. no or partial ownership, the degree to which vegetation on the parcel was regulation). The term “regulation” includes all sorts of tended, etc.); (2) the presence/absence of Tromsø palm on the measures that can be taken to prevent the spread of respondents’ parcel;(3)thedegreeofregulationofTromsø Tromsø palm, such as cutting of stems, cutting of flowers, palm on the parcel, the handling of the plant material after digging out roots, mowing, or using an herbicide. removal, the responsible person; (4) landowners’ evaluations of the aesthetic, health-related, and symbolic value of Tromsø Statistical Analyses. Univariate, bivariate, and multivariate palm (identified as important values from the interviews) and analyses were conducted by using IBM SPSS Statistics v. 20. normative beliefs regarding the regulation of Tromsø palm on Logistic regressions were used to determine which independent Tromsø Island; and (5) sociodemographic information about variables (sociodemographic variables, parcel characteristics, the respondent. landowner values and normative beliefs) were associated most The questionnaire referred to the most recent vegetation strongly with the outcome variables regarding Tromsø palm period (May–September 2012), also corresponding to the regulation. We conducted both binary and multinomial field observations. The respondents were asked to refer to logistic regressions to account for the two different ways to the whole parcel in their answers, even if they only owned categorize outcomes of Tromsø palm regulation on the parcels parts of a parcel and shared it with other owners. On the (cf. Field 2009; Singh 2007). The binary method considered cover letter of the survey, a Web link was provided to an two possible outcomes: parcels from where Tromsø palm online version of the survey, which served as an alternative (1) has or (2) does not have the potential to spread to other option for the respondents. Together with a cover letter and parcels, which included the whole dataset including parcels a prepaid return envelope, the questionnaires were mailed to with no Tromsø palm as not having the potential to spread. all 441 landowners of the sample parcels, with a follow-up The multinomial method only considered parcels where the reminder by mail after 6 wk. owners were aware of Tromsø palm’s presence on their Considering undeliverable addresses (14) and respon- parcel, with three possible outcomes: Tromsø palm was (1) dents who claimed they were not able to answer (because, not, (2) partially, or (3) fully regulated. for instance, they had never been to the parcel) (3), the For each regression type, two models were run, so four effective sample size was 424. The response rate was 47% regression models were developed: a binary logistic regres- (n = 201). Since two respondents indicated that the parcels sion model (model I) and a multinomial logistic regression were partially publicly owned or company owned, 199 model (model II), each including the independent variable questionnaires were included in the analysis. Some classifi- “frequency of tending the vegetation-covered area on cations of parcels (“with” or “without” Tromsø palm) were parcel”; and another binary (model III) and multinomial revised based on the landowners’ answers; for instance, if a regression model (model IV), each including instead the parcel appeared to have no Tromsø palm during field independent variable “residence status: owners lived on the checks, but the owner indicated Tromsø palm was present, parcels vs. only renters lived on the parcels vs. no residence then that parcel was classified as a parcel with Tromsø palm. on the parcels.” Two models of both the regression types However, if the plant had been observed on the parcel were developed, because the variables “frequency of tending during field checks, but the respondent indicated it was not the vegetation-covered area on the parcels” and “residence present, the parcel was nevertheless classified as a parcel with status” could not be included in a single model, as the other Tromsø palm. In the few cases where the presence or variables in the model became non-significant, likely due to absence of the plant on the parcel was unproven based on a small sample size. The models with the independent the field visits, the respondents’ answers were considered variable “frequency of tending the vegetation-covered area” valid. In cases in which owners did not know whether the (models I and II) showed the highest number of significant plant was on their parcels, the field observations were results and therefore are primarily discussed in this paper. In considered valid. There was only one parcel for which the all four regression models, outliers were removed according status of Tromsø palm could not be determined. to Field (2009).

Meier et al.: Regulation of H. persicum by Private Landowners • 171

Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 27 Sep 2021 at 18:01:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/inp.2017.11 Results and Discussion associated with the regulation degree of Tromsø palm on the landowners’ parcels (no, partial, or full regulation) in mul- Respondents’ and Parcels’ Characteristics. Tables 1 tinomial logistic regression analyses. As outlined in the (continuous and ordinal variables), 2, and 3 (categorical “Materials and Methods,” four models were developed, but variables) summarize the sociodemographic variables of the models I and II, which showed the highest number of sig- questionnaire respondents, the characteristics of their parcels, nificant results, are mainly discussed here. When variables and their evaluations of Tromsø palm’s values and of their were significant in both the binary (model I) and multi- normative beliefs regarding Tromsø palm’s regulation on nomial logistic regression (model II), only the results of the Tromsø Island. As many respondents did not answer all binary logistic regression are presented. The results of the questions, the total number of observations was different for multinomial model are discussed only if variables proved to each variable (max. 199, see “Data Collection”). Regarding be significant exclusively in the multinomial logistic regres- parcel characteristics, almost all respondents were owners of sion. Furthermore, bivariate analyses were conducted their parcels; only one respondent was a renter (Table 2). regarding regulation behavior and the different variables. Therefore, “landowner” is used as a synonym for “respon- Only those significant results of the bivariate statistics that dent” in the following sections. were either not significant in the regressions or showed a different direction are presented in this paper. In some cases Predictors for Tromsø Palm’s Status on Landowners’ of bivariate statistics, the sample sizes were too small to Parcels. This section presents and discusses how socio- apply Chi-square tests. demographic characteristics, parcel characteristics, values, The Nagelkerke pseudo-R2 values in the binary logistic and normative beliefs were associated with Tromsø palm’s regression models were 0.194 for the binary model I potential to spread as seen with the binary logistic regression (n = 176) and 0.145 for the binary model III (n = 178), analysis. Furthermore, it is shown how the variables were while the values were 0.365 for the multinomial model II

Table 1. Studied variables (part 1): respondents’ (landowners’) sociodemographic characteristics, parcel characteristics, values, and normative beliefs.

n Variable Min Max Mean Median SD (total) Sociodemographic characteristics Age (years) 20 93 57.16 59 14.715 194 Household income in 2011a 1 5 3.64 4.0 1.179 146 Number of persons living in respondent’s household 1 14 2.69 2.0 1.519 194 Years respondent lived in Tromsø (residence time) <1 85 40.91 40 19.317 196 Parcel characteristics Years of parcel ownership 1 96 21.58 18.0 16.003 192 Frequency of tending the vegetation-covered area on parcels between 1 6 3.97 4.0 1.463 192 May and September 2012b Evaluation of valuesc Aesthetic value 1 5 3.19 3.0 1.351 195 Health value 2 5 3.62 3.0 0.766 195 Symbolic value 1 5 2.8 3 1.415 194 Evaluation of normative beliefsd Occurrence of Tromsø palm on Tromsø Island 1 5 3.66 4.0 1.170 195 Necessity of control measures against Tromsø palm on Tromsø Island 1 5 4.25 5.0 1.020 194 a Attributes of income: 1: less than 300,000 Norwegian kroner (NOK); 2: 300,000–450,000 NOK; 3: 450,000–600,000 NOK; 4: 600,000–1,000,000 NOK; 5: more than 1,000,000 NOK. b Attributes of frequency of tending the vegetation (e.g., cutting hedges, mowing, weeding): 1: never; 2: less than once per year; 3: once per month; 4: several times per month; 5: once per week; 6: several times per week. c Attributes of evaluation of values: Aesthetic value (appearance of Tromsø palm), 1: ugly to 5: nice. Health value (health impact of Tromsø palm) 1: positive impact to 5: negative impact. Symbolic value (symbolic importance of TP for Tromsø), 1: not important to 5: important. d Attributes of evaluation of normative beliefs: occurrence of Tromsø palm on Tromsø Island: 1: do not perceive Tromsø palm as a problem on Tromsø Island to 5: perceive Tromsø palm as a problem on Tromsø Island. Necessity of regulation measures (done by institutions) against Tromsø palm on Tromsø Island, 1: not necessary to 5: necessary.

172 • Invasive Plant Science and Management 10, April–June 2017

Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 27 Sep 2021 at 18:01:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/inp.2017.11 Table 2. Studied variables (part 2): respondents’ (landowners’) sociodemographic characteristics and parcel characteristics.

n Variable Proportion (%) n (total) Sociodemographic characteristics Gender Male/female 50.0/50.0 96/96 192 Education With higher education (fulfilled university degree or 69.4/30.6 134/59 193 polytechnical high school)/without higher education Permanent injuries Experienced permanent injuries (e.g., a scar from Tromsø 19.5/80.5 38/157 195 palm [including knowing somebody who was affected]/ had not experienced permanent injuries Parcel characteristics Respondent status Respondent was owner/renter 99.5/0.5 198/1 199 Residence status Owners (in some cases along with renters) lived on parcel/ 83.8/9.9/6.3 160/19/12 191 only renters lived on parcel/no residence on parcel Children (<10 yr) Lived/did not live on parcel 23.5/76.5 42/137 179 Households Parcel associated with one household/several households 65.8/34.2 125/65 190 (jointly owned) Normative belief Degree Tromsø palm should be Full removal (eradication)/partial removal (from some 33.0/64.3/2.7 60/117/5 182 removed (by local authorities) areas)/no removal anywhere from Tromsø Island

(n = 120) and 0.260 for the multinomial model IV To summarize, parcels from which Tromsø palm does (n = 120). These values are not too low, considering that not have the potential to spread (having no or fully regulated these variables measure human behavior. The R2 values are Tromsø palm) compared with parcels where Tromsø palm somewhat higher in the multinomial models II and IV, has the potential to spread (not or partly regulated) tend to which means the variables in these models fit the regression have the following characteristics (based on the binary better compared with the binary models I and III. However, logistic regression, model I [Table 4] and model III): a more this might not be related to the fact that the variables in the frequently tended vegetation-covered area (only model I); multinomial models explain the outcome better compared owners who live on the parcel compared with only renters or with the binary models, but rather that the data set used for no residents (only model III); only one household is the multinomial models is different (a subset of the data responsible for the parcel compared with several; more used for the binary models). people live in the respondent’s household (only model I);

Table 3. Studied variables (part 3): the outcome variables of the regression analyses.

n Variable Proportion (%) n (total) Regulation behavior Tromsø palm’s potential to spread between Plant fully regulated or absent/plant 55.6/44.4 110/88 198 May and September 2012a partly or not regulated Degree Tromsø palm was regulated between Parcel with full regulation/partial 44.3/35.7/20.0 62/50/28 140 May and September 2012b regulation/no regulation a This is the outcome variable of the binary logistic regression. For one parcel, the status of Tromsø palm on the parcel was not known; therefore, the binary regression included 198 parcels instead of 199. b This is the outcome variable of the multinomial logistic regression. These analyses included only parcels from those landowners who knew that they had Tromsø palm on their parcels between May and September 2012. Full regulation: no plant flowered on the parcel; partial regulation: at least one plant flowered on the parcel; no regulation: there were no measures against Tromsø palm in that period.

Meier et al.: Regulation of H. persicum by Private Landowners • 173

Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 27 Sep 2021 at 18:01:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/inp.2017.11 https://doi.org/10.1017/inp.2017.11 Downloaded from 174 https://www.cambridge.org/core • naiePatSineadMngmn 0 April 10, Management and Science Plant Invasive

Table 4. Significant variables affecting probability of potential of Tromsø palm (TP) to spread on Tromsø Island (left column) and TP being regulated partially (at least one plant flowered on the parcels) or fully (no plant flowered on the parcels) (middle and right columns).

Outcome variable of binary logistic regression (model I)c Outcome variables of multinomial logistic regression (model II)d . IPaddress: TP was fully regulated or absent on TP was partially regulated on TP was fully regulated on respondent’s parcel respondent’s parcel respondent’s parcel 170.106.34.90 Independent variablesb B SE P-value Odds B SE P-value Odds B SE P-value Odds

Constant (model I)/intercept (model II) −4.461 0.908 0.000 0.012 −8.761 2.250 0.000 — −9.258 2.271 0.000 — ’ < , on Frequency parcel s vegetation was tended 0.348 0.119 0.003 1.416*** 0.917 0.265 0.001 2.501*** 1.058 0.264 0.001 2.881***

27 Sep2021 at18:01:12 (1: never; 6: several times per week from May to September 2012) Residence status (reference: only renter(s) on parcel) 0.025 − − – Owner(s) lived on parcel 1.138 0.652 0.081 3.121* 1.441 1.211 0.234 0.237 0.639 1.232 0.604 0.528 ue2017 June No residence on parcel −0.435 0.944 0.645 0.647 −3.584 1.664 0.031 0.028** −3.356 1.694 0.048 0.035** No. of households associated with parcel: ——— —1.623 0.697 0.020 5.068** 0.702 0.686 0.307 2.017 Several households (reference: one household) One household (reference: several households) 0.831 0.357 0.020 2.294** ——— — ——— — , subjectto theCambridgeCore termsofuse,available at Length of parcel ownership ——— —0.057 0.026 0.029 1.059** 0.037 0.026 0.147 1.038 No. of persons living in respondent’s household 0.378 0.138 0.006 1.460*** ——— — ——— — Evaluating TP’s occurrence on Tromsø Island 0.486 0.151 0.001 1.626*** ——— — ——— — (1: not perceived as problem; 5: perceived as problem) Evaluating the necessity of regulating TP on Tromsø Island ——— —1.028 0.332 0.002 2.796*** 1.262 0.340 <0.001 3.531*** (1: not necessary; 5: necessary) a Both models refer to the period between May and September 2012. b Bivariate analysis showed that on parcels where TP was partially regulated, there was a higher percentage belonging to the category of not being inhabited by children below the age of 10 compared with parcels inhabited by children. However, the inclusion of the variable “children (<10 yr) lived/did not live on the parcel with residence” made other variables non-significant in the multinomial logistic regressions; therefore, it was left out. The variable “residence status” was run in separate binary (model III) and multinomial (model IV) logistic regression models including all the variables except “Frequency the vegetation-covered area on the parcels was tended.” c Nagelkerke pseudo-R2 = 0.194 (maximum: 1.0), n = 176, reference category: “Tromsø palm was partly regulated/not regulated on the parcels”; no outlier removed. d Nagelkerke pseudo-R2 = 0.365 (maximum 1.0), n = 120, reference category: “no regulation of Tromsø palm on parcels”; two outliers removed.

https://www.cambridge.org/core/terms *** Significant at 0.01; ** significant at 0.05; * significant at 0.1. . and the respondent holds the normative belief that Tromsø palm, compared with uninhabited parcels. Having a resident palm’s occurrence is a problem on Tromsø Island. on the parcel was significantly associated with tending the Considering only those landowners who had (and were aware vegetation-covered area more frequently in bivariate analysis of) Tromsø palm on their parcels, full and/or partial regulation (Kruskal-Wallis test: P < 0.001, n = 190). of Tromsø palm, compared with no regulation, was associated During field visits, it could be seen that on parcels with those parcels (based on the multinomial logistic regression, without residents (no buildings or empty buildings for sale), model II [Table 4] and model IV) that had only renters Tromsø palm often spread unchecked. Much Tromsø palm compared with being uninhabited (only model IV), were owned was found in an undeveloped area at the shore. In an for a longer time, and the respondent holds the normative belief interview, the owner of this plot said she did not tend the that regulation measures against Tromsø palm are necessary on vegetation there because she planned to sell the parcel to Tromsø Island. In contrast to the binary logistic regression the municipality, and she did not know that Tromsø result, the multinomial regression model II showed that parcels palm was on the plot. Similarly, Fischer and Charnley shared between several households (as compared with those with (2012) found that forest landowners who are living on their just one household) had a higher probability of having Tromsø parcels have a higher probability of regulating invasive palm partly regulated compared with it not being regulated. plants on their properties, and the authors assumed that Using the same data set of landowners who had (and were aware living on the parcels makes it easier for the landowners of) Tromsø palm on their parcels, bivariate analysis (Chi-square to tend their properties and to regulate the growth of test) showed that residential parcels without children (younger invasive plants. than 10 yr) more often had partly regulated Tromsø palm The binary regression (model I and III) showed that compared with residential parcels with children, which more parcels associated with just one household significantly often had unregulated Tromsø palm. more often tended to have plots that were fully regulated The significant result that a higher frequency of regulating or had no Tromsø palm, compared with jointly owned the vegetation-covered areas is associated with having no plots. However, the multinomial regression (model II) Tromsø palm or fully regulated Tromsø palm can also be showed that jointly owned parcels significantly tended supported by field observations. They showed that parcels with to have a higher percentage of partially regulated than mown lawns and cut hedges generally had less Tromsø palm. nonregulated Tromsø palm, as compared with single- The almost significant findingthatnoTromsøpalmorfully household plots. regulated Tromsø palm is more commonly found on parcels Having jointly owned parcels could be an advantage for at inhabited by their owners, as compared with those inhabited by least partially regulating Tromsø palm, as there are more renters (binary model III, reference level: “only renter(s) lived people who can do some garden work, and there is often on parcel”), was also encountered in interviews with a community work on shared parcels (this is a Norwegian landownerandarenter:oneownerinthequestionnairegave custom called a dugnad), which had been indicated by one as a reason why Tromsø palm was not tended that the renter questionnaire respondent from a jointly owned parcel. was responsible for the vegetation on the parcel but was not However, one-household parcels seem to obtain better doing anything. In another case, it was found in an interview results in regulating Tromsø palm so thoroughly that it does that a renter saw the responsibility as lying with her landlord, not spread. Probably, on jointly owned parcels, there is a who did not feel responsible. Although the findingisonlynear lack of one person/family feeling the complete obligation significant (P = 0.081), it could represent an effect, because the toward managing the parcel, because the more people are sample size generally was small. present in a problematic situation, the less each individual Furthermore, differences in parcels with and without any often feels responsible to solve the problem (Bell et al. resident(s) were investigated. Compared with uninhabited 2001). Furthermore, on jointly owned parcels, landowners parcels, plots where the owners lived tended to have might not know which part they are responsible for and significantly more fully regulated or absent Tromsø palm (a therefore regulate Tromsø palm only partially. Additionally, version of binary model III with “no residence on parcel” as jointly owned parcels could be larger than single-household the reference level, P = 0.029, odds = 4.823). Additionally, parcels and may be less easy to manage. In this context, the running the multinomial model IV (reference level: “only effect of the parcel size on the regulation of Tromsø palm renter(s) lived on parcel”), parcels where only renters lived could be examined in a further study, although Fischer and had significantly more partly1 (P = 0.031, odds = 35.714) Charnley (2012) found no impact of parcel size on the or fully2 (P = 0.048, odds = 28.571) regulated Tromsø regulation behavior of forest landowners. The longer a parcel is owned, the significantly higher is

1 the probability that the plant is regulated partly or even fully As parcels where only renters lived was the reference level, the inverse of the odds for the parcels without residence (Table 4) corresponded to the odds of the parcels (multinomial models II and IV); a possible explanation with only renters: 35.714 = 1/0.028. could be that it takes several years of consistent regulation 228.571 = 1/0.035 (Table 4). measures to remove H. persicum (Nielsen et al. 2005).

Meier et al.: Regulation of H. persicum by Private Landowners • 175

Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 27 Sep 2021 at 18:01:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/inp.2017.11 Also, respondents who have owned land for a longer time key informants, e.g., from Tromsø University: “People have might be more interested in taking care of the land. mixed feelings […]. Sometimes they like it and think it is a Bivariate analysis showed that a significantly higher bit impressive in a way because it is so large and they like to percentage of residential parcels where children (younger than take pictures of it in the winter when the dry stems are 10 yr) lived were not regulated for Tromsø palm: 33.3% of decorative and so forth. But they do not want to have [the child-inhabited parcels (n = 8) vs. 13.9% for no-child parcels plant] in their own garden.” (n = 14); whereas a higher percentage of (residential) parcels Contrary to some of the normative beliefs, none of the where no children lived were partly regulated: 41.6% for values investigated in this study (aesthetic, health-related, parcels with no children (n = 42) vs. 20.8% of parcels with and symbolic) were significant in any of the four regression children (n = 5) (there was no difference regarding full models. The normative beliefs are more directly associated regulation) (Chi-square test: P = 0.041, n = 125). This result with the topic “regulation of Tromsø palm” and therefore was unexpected, as it was assumed that parents might be more might have more influence on the regulation behaviors of vigilant in controlling Tromsø palm to protect their children landowners than general values of the plant (cf. Ajzen and from the phototoxic sap. The inclusion of the variable Fishbein 1977). “children’s presence or absence on the parcels” into the regression models led to the non-significance of other included Additional Findings Regarding Tromsø Palm’s Spread variables, and therefore this variable was omitted. and Regulation. Regarding the question “How was the More persons living in a household was associated with plant material of Tromsø palm handled after it was having fully regulated or no Tromsø palm on the parcel removed? (mark all answers that apply),” most respondents (binary model I). A reason might be that larger households (the question was answered by those who either partially or offer more workforce to take care of Tromsø palm. Other fully regulated Tromsø palm on their parcels) indicated that sociodemographic variables (such as age, gender, income, the plant waste was disposed on the parcel, either in a = = time period of being resident in Tromsø, education) or compost heap (43.8%, n 49, ntotal 112) and/or on the having incurred injuries due to Tromsø palm were not found ground (32.1%, n = 36). Fewer respondents indicated that to be significantly related to the potential of the Tromsø palm the plant waste was taken away from the parcel and depos- to spread or to the degree of Tromsø palm regulation. ited in the garbage/organic waste container (24.1%, Respondents who hold the normative belief that Tromsø n = 27) and/or the municipal waste disposal site (10.7%, palm’s occurrence on Tromsø Island is a problem were n = 12). Leaving the plant waste on the parcel must be significantly associated with owning parcels where Tromsø regarded as unfavorable, as it can contribute to the con- palm is fully regulated or absent (binary model I and III). The tinued spread of the plant, which has been shown in the case multinomial regression models II and IV showed that those of giant hogweed (Pyšek et al. 2007a). who regulated the plant at least partly or fully were To answer the question “How did/does Tromsø palm significantly associated with holding the normative belief end up on your parcel? (mark all answers that apply),” = = that regulation measures for Tromsø palm on Tromsø Island 37.9% (n 53, ntotal 140) of all respondents who had are necessary. This is comparable to the findings of Daab and Tromsø palm on their parcels indicated that it spread from Flint (2010) and Fischer and Charnley (2012) that being neighboring parcels, while 26.4% assumed it spread from worried about invasive species is related to landowners roadsides (n = 37). This shows that a number of respon- regulating invasive plants on their own properties. dents felt they had to deal with a constant intrusion of plants There was no significant association in how landowners from adjacent areas. Field observations revealed that if indicated their normative beliefs toward the degree Tromsø Tromsø palm existed on a parcel, it could often be found on palm should be removed from Tromsø Island by institutions neighboring parcels as well. During fieldwork, it was and the landowners’ regulation behaviors on their parcels observed that Tromsø palm was often growing along parcel (however, for the Chi-square tests, the number of borders—possibly because the responsibilities for these areas respondents favoring no removal was below five, so they were not clear—and Tromsø palm was often found in were excluded from this test, and it was therefore not inaccessible or steep areas on parcels. The results of the other possible to make a statement about these respondents). answer options for the question regarding how Tromsø These results might show that Tromsø palm is evaluated palm ended up on the parcel are beyond the scope of this differently depending on whether the question refers to the paper and therefore not presented here. plant that grows on the landowners’ parcels or to Tromsø palm in general. This phenomenon was also found during Implications for Tromsø Palm Management on Private an interview with a landowner who mentioned that she had Parcels. Many landowners may leave their parcels for removed the plant completely from her parcel, but at the vacation for several weeks during the summer months, so same time she appreciated it along the roads and the shore. there are generally fewer people available to tend the private This duality of some locals’ evaluation was mentioned by all land at the time when Tromsø palm flowers and seeds.

176 • Invasive Plant Science and Management 10, April–June 2017

Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 27 Sep 2021 at 18:01:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/inp.2017.11 Because of this and the factors mentioned in the previous not aiming at eradicating the species but controlling it, as section, help from public authorities seems necessary for invasive species management is an open-ended process. In control. According to the results of this study, private this way, the study might give some hints as to which private landowners who will most likely need support from autho- areas the authorities could target. rities if resources were available might be, for instance, those who own parcels without residents. These parcels can pre- Potential Bias in the Study. Selecting key informants sent problems, as the successful management of the plant by snowball sampling is considered the most appropriate demands active and consistent control. The owners of these method if the total study population is not known (Faugier fi parcels could receive nancial incentives or active help from and Sargeant 1997), and some participants might have more fi authorities. Furthermore, the municipality could bene tby knowledge than others (Marshall 1996). However, accord- targeting landowners who recently bought their parcels and ing to Griffiths et al. (1993), this selection method might help them through education and assistance in controlling lead to a sample that is biased toward the worldview of those fi the plant during the rst years of ownership. In addition, key informants who provided the most contacts for further owners of parcels that are jointly owned are appropriate informants, because potential informants not known by the fi candidates to receive active or nancial help, because they key informants had a lower likelihood of being included in were found to have problems regulating the plant fully or the study. To minimize this bias, care was taken to continue removing it. Authorities could also try to get permission to find and interview key informants until a wide range of from landowners to regulate the plant on private land close opinions, worldviews, and people from different professions to public areas to prevent the plant from spreading onto were included in the sample. public land. Additionally, densely populated areas could be In 92 of 199 answered questionnaires, there were missing the focus of regulation measures to minimize health risks. answers. Seven respondents even seemed to have overlooked fi The nding that landowners who consider the plant as whole pages of the questionnaire due to the brochure problematic on Tromsø Island also regulated the plant more format. Moreover, there was a small sample size for parcels could imply that education and information campaigns without a residence (12 of 191 respondents who answered about the negative effects of invasive species could motivate this question), and it was therefore difficult to get clear private landowners to take action. In addition, landowners results about differences between parcels with and without could be better informed about disposal of cut plant parts in residents. garbage bins or at the municipal waste disposal site to prevent further spread, based on findings about giant hogweed seed ripening by Pyšek et al. (2007a). Authorities Acknowledgements should also inform landowners about taking particular care of border areas and hidden or inaccessible spaces in their We thank the many landowners and renters in Tromsø who information campaigns and assistance programs. These contributed to the study. We would also like to thank the key programs could be delivered through leaflets and neighbor- informants from Tromsø Municipality (Tromsø Kommune), hood meetings where neighbors would have the opportunity Troms County governor (Fylkesmannen i Troms), Norwegian to coordinate the regulation. National Road Administration in Tromsø (Statens vegvesen), Key informants from Tromsø University and GWN did University of Tromsø, and the Tromsø Arts Association not believe that the Tromsø palm could be eradicated from (Kunstforeningen Tromsø), and the other residents who agreed Tromsø Island, and the key informant from Tromsø to be interviewed. Thanks also to Harald Hals Karlsen for University was concerned that measures would require a translating the questionnaire into Norwegian. Special thanks we lot of resources. Gardener et al. (2010) investigated the owe to the anonymous reviewers for their valuable comments success of eradication efforts against invasive plants in the on earlier versions of the manuscript. The German Academic fi Galapagos. Based on their results, it might be dif cult to Exchange Service, the Department of International Environment regulate the plant on private areas on Tromsø Island because and Development Studies at Norwegian University of Life many landowners are involved. There will always be Sciences, and the Norwegian Institute of Bioeconomy Research landowners who do not voluntarily regulate Tromsø palm provided financial support for the project (RCN grant nos. rigorously enough, and there might be areas on a parcel 194052 and 194051). where the plant is more difficult to regulate. Therefore, the plant will always find places where it can grow and from which it can spread. Furthermore, Gardener et al. (2010) found that if invasive plants are too widespread and well Literature Cited established, eradication might no longer be possible. In such Aitken M, Rangan H, Kull CA (2009) Living with alien invasives. The situations, Rotherham and Lambert (2011) believe that political ecology of wattle in the eastern highveld Mpumalanga South management of invasive species needs to be more pragmatic, Africa. Études Océan indien 42–43:115–141

Meier et al.: Regulation of H. persicum by Private Landowners • 177

Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 27 Sep 2021 at 18:01:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/inp.2017.11 Ajzen I, Fishbein M (1977) Attitude-behavior relations: a Hansen S (2014) Lager suppe av Tromsøpalmen [Preparing soup of theoretical analysis and review of empirical research. Psychol Bull Tromsø palm] iTromsø. http://www.itromso.no/nyheter/ 84:888–918 article9810579.ece, accessed April 29, 2017 Alm T (2006) Tromsø palm i folketradisjonen [Tromsø palm and Haugen BSH (2006) Norsk bunadleksikon: Alle norske bunader og traditions]. Ottar 261:18–24. Norwegian samiske folkedrakter [Encyclopedia of Norwegian Local Costumes: Alm T (2013) Ethnobotany of Heracleum persicum Desf. ex Fisch., an All Norwegian and Sami Local Costumes]. Oslo: Damm. 399 invasive species in Norway, or how plant names, uses, and other p. Norwegian traditions evolve. J Ethnobiol Ethnomed 9:42 Hemati A, Azarnia M, Angaji SA (2010) Medicinal effects of Heracleum Alm T, Jensen C (1993) Tromsøpalmen (Heracleum laciniatum auct. persicum (Golpar). Middle East J Sci Res 5:174–176 scand.)—noen kommentarer til artens innkomst og ekspansjon i Nord- Hodkinson DJ, Thompson K (1997) Plant dispersal: the role of man. Norge [Heracleum laciniatum auct. scand.—notes on its introduction and J Appl Ecol 34:1484–1496 expansion in northern Norway]. Blyttia 51:61–69 Homer PM, Kahle LR (1988) A structural equation test of Alm T, Jensen C, Often A (2006) Tromsøpalmens historie [History of the value-attitude-behavior hierarchy. J Pers Soc Psychol 54: Tromsø palm]. Ottar 261:3–9. Norwegian 638–646 Alm T, Often A (2006) Tromsøpalmen og dens slektninger—et knippe Jahodová S, Trybush S, Pyšek P, Wade M, Karp A (2007) Invasive pestplanter [Tromsø palm and its relatives—a collection of pest species of Heracleum in Europe: An insight into genetic relationships plants]. Ottar 261:10–17. Norwegian and invasion history. Divers Distrib 13:99–114 Bell PA, Greene TC, Fisher JD, Baum A (2001) Environmental Junttila O (1975) Allelopathy in Heracleum laciniatum: inhibition of Psychology. Fort Worth, TX: Harcourt College Publishers. 634 p lettuce seed germination and root growth. Physiol Plant 33:22–27 Blossey B (1999) Before, during and after: the need for long-term monitoring Kavli G, Volden G (1984) Phytophotodermatitis. Photodermatology in invasive plant species management. Biol Invasions 1:301–311 1:65–75 Bright AD, Manfredo MJ (1996) A conceptual model of attitudes toward Kavli G, Volden G, Midelfart K, Haugsbø S, Prytz JO (1983a) natural resource issues: a case study of wolf reintroduction. Hum Phototoxicity of Heracleum laciniatum. Case reports and experimental Dimens Wildl 1:1–21 studies. Contact Dermatitis 9:27–32 Daab MT, Flint CG (2010) Public reaction to invasive plant Kavli G, Volden G, Midelfart K, Krokan H, Prytz JO, Haugsbø S species in a disturbed Colorado landscape. Invasive Plant Sci Manag (1983b) In vivo and in vitro phototoxicity of different parts of 3:390–401 Heracleum laciniatum. Contact Dermatitis 9:269–273 [EPPO/OEPP] European and Mediterranean Plant Protection Organiza- Kellert SR (1996) The Value of Life: Biological Diversity and Human tion/Organisation Européenne et Méditerranéenne pour la Protection Society. Washington, DC: Island Press. 263 p des Plantes (2009) Heracleum mantegazzianum, Heracleum sosnowskyi Kollmuss A, Agyeman J (2002) Mind the gap: why do people act and Heracleum persicum. European and Mediterranean Plant Protec- environmentally and what are the barriers to pro-environmental tion Organization (EPPO) data sheet on invasive alien plants. Bull behavior? Environ Educ Res 8:239–260 OEPP 39:489–499 Lid J, Lid DT (2005) Norsk flora [Norwegian Flora]. Oslo: Samlaget. Faugier J, Sargeant M (1997) Sampling hard to reach populations. J Adv 1230 p. Norwegian Nurs 26:790–797 Marshall MN (1996) Sampling for qualitative research. Fam Pract Field A (2009) Discovering statistics using SPSS. London: Sage. 821 p 13:522–525 Fischer AP, Charnley S (2012) Private forest owners and invasive plants: risk McNeely JA (2001a) Preface. Pages 1–2 in McNeely JA, ed. The Great perception and management. Invasive Plant Sci Manag 5:375–389 Reshuffling: Human Dimensions of Invasive Alien Species. Gland, Fishbein M, Ajzen I (1975) Belief, attitude, intention, and behavior: Switzerland/Cambridge, UK: IUCN an introduction to theory and research. Reading, MA: Addison- McNeely JA (2001b) An introduction into human dimensions of invasive Wesley. 578 p alien species. Pages 5–20 in McNeely JA, ed. The Great Reshuffling: Fröberg L (2010) Heracleum L. Pages 224–234 in Jonsell B & Karlsson T, eds. Human Dimensions of Invasive Alien Species. Gland, Switzerland/ Flora Nordica Volume 6, Thymelaeaceae to Apiaceae. Stockholm: Swedish Cambridge, UK: IUCN Museum of Natural History McNeely JA, Mooney HA, Neville LE, Schei PJ, Waage JK (2001) Gardener MR, Atkinson R, Rentería JL (2010) Eradications and people: Global Strategy on Invasive Alien Species. Gland, Switzerland/ Lessons from the plant eradication program in Galapagos. Restor Ecol Cambridge, UK: IUCN, Global Invasive Species Programme. 63 p 18:20–29 Myrås H, Junttila O (1981) Interaction between Heracleum laciniatum Gederaas L, Moen TL, Skjelseth S, Larsen LK (2012) Fremmede arter i and some other plants. Holarctic Ecol 4:43–48 Norge—med norsk svarteliste 2012 [Invasive species in Norway— Nielsen C, Ravn HP, Nentwig W, Wade M, eds (2005) The Giant with the Norwegian blacklist 2012]. Trondheim: Artsdatabanken. Hogweed Best Practice Manual: Guidelines for the Management and 212 p. Norwegian Control of an Invasive Weed in Europe. Hørsholm, Denmark: Forest Google Earth 7.1.1. (2013) Tromsø Island, 69°40'06.75''N, 18° & Landscape Denmark. 44 p 56'18.01''E. elevation 0–160m. Google Nilsen EW (1991) Tromsøpalmen [The Tromsø palm]. Polarflokken Google Maps (2017) Tromsø Island, 69°40'06.75''N, 18°56'18.01''E. 15:149–150. Norwegian http://maps.google.com/. Accessed: April 29, 2017 Often A, Graff G (1994) Skillekarakterer for kjempebjørnekjeks— Griffiths P, Gossop M, Powis B, Strang J (1993) Reaching hidden Heracleum mantegazzianum—og tromsøpalme—H. ‘laciniatum’ populations of drug users by privileged access interviewers: methodo- [Characteristics separating Heracleum mantegazzianum and H. ‘laci- logical and practical issues. Addiction 88:1617–1626 niatum’]. Blyttia 52:129–133. Norwegian

178 • Invasive Plant Science and Management 10, April–June 2017

Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 27 Sep 2021 at 18:01:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/inp.2017.11 Pyšek P (1998) Alien and native species in Central European urban floras: Schlesselman JJ (1982) Case-Control Studies: Design, Conduct, Analysis. a quantitative comparison. J Biogeogr 25:155–163 New York: Oxford University Press. 359 p Pyšek P, Krinke L, Jarošik V, Perglová I, Pergl J, Moravcová L (2007a) Timing Singh K (2007) Quantitative Social Research Methods. New Delhi: Sage. and extent of tissue removal affect reproduction characteristics of an invasive 432 p species Heracleum mantegazzianum. Biol Invasions 9:335–351 Statistics Norway (2016) Population, by Basic Statistical Unit. http://www. Pyšek P, Perglová I, Krinke L, Jarošik V, Pergl J, Moravcová L statistics.no/statistikkbanken/SelectVarVal/Define.asp?MainTable= (2007b) Regeneration ability of Heracleum mantegazzianum and FolkGrunnkrKom&KortNavnWeb=folkemengde&PLanguage=1& implications for control. Pages 112–125 in Pyšek P, Cock MJW, checked=true. Accessed: April 29, 2017 Nentwig W & Ravn HP, eds. Ecology and Management of Giant Tromsø Municipality (2015) Heracleum Nursing Home. http://www. Hogweed (Heracleum mantegazzianum). Wallingford, UK: CABI tromso.kommune.no/heracleum.121288.no.html. Accessed: April 29, Qvenild M, Setten G, Skår M (2014) Politicising plants. Invasive alien 2017 species and domestic gardening. Nor J Geogr 27:10–12 van Wilgen BW (2012) Evidence, perceptions, and trade-offs associated Renna R (2002) Bekjemping av tromsøpalme—en håpløs oppgave? [Fighting with invasive alien plant control in the Table Mountain National Park, Tromsø palm—a hopeless task?]. Polarflokken 26:101–102. Norwegian South Africa. Ecol Soc 17:23 Richardson DM, Pyšek P, Rejmánek M, Barbour MG, Panetta FD, West Vaske JJ, Donnelly MP (1999) A value-attitude-behavior model CJ (2000) Naturalization and invasion of alien plants: concepts and predicting wildland preservation voting intentions. Soc Natur Resour definitions. Divers Distrib 6:93–107 12:523–537 Rijal DP, Alm T, Jahodová S, Stenøien HK, Alsos IG (2015) Zajdela F, Bisagni E (1981) 5-Methoxypsoralen, the melanogenic Reconstructing the invasion history of Heracleum persicum (Apiaceae) additive in sun-tan preparations, is tumorigenic in mice exposed to into Europe. Mol Ecol 24:5522–5543 365 nm u.v. radiation. Carcinogenesis 2:121–127 Rokeach M (1979) Understanding human values: individual and societal. Zinn HC, Manfredo MJ, Vaske JJ, Wittmann K (1998) Using normative New York: Free Press. 322 p beliefs to determine the acceptability of wildlife management actions. Rotherham ID, Lambert RA (2011) Good science, good history Soc Nat Resour 11:649–662 and pragmatism: managing the way ahead. Pages 355–365 in Rotherham ID & Lambert RA, eds. Invasive and Introduced Plants and Received January 22, 2016, and approved January 31, 2017. Animals. Human Perceptions, Attitudes and Approaches to Management. London: Earthscan Associate Editor for this paper: John A. Randall, University of California, Saldaña J (2013) The Coding Manual for Qualitative Researchers. Davis. London: Sage. 303 p

Meier et al.: Regulation of H. persicum by Private Landowners • 179

Downloaded from https://www.cambridge.org/core. IP address: 170.106.34.90, on 27 Sep 2021 at 18:01:12, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/inp.2017.11